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Document prepared by AdelaideAqua and HATCH-SMEC Report – Intake and Outfall Systems Environmental Performance SummaryFor Adelaide Desalination Project (ADP) H332401-1000-05-124-0090 Rev 2 Page 2

Table of Contents

1

Introduction ....................................................................................................................................8 2 Environmental Objectives and Performance Criteria...................................................................10

2.1 Conditions of Development Authorisation Gazetted 11th June 2009 (DA Conditions)......10 2.2 ADP Environmental Impact Statement (EIS).....................................................................12

3 Intake Structure............................................................................................................................16

3.1 Intake Design Overview.....................................................................................................16 3.2 Intake Location ..................................................................................................................16 3.3 Subtidal Reef .....................................................................................................................17 3.4 Intake Velocity ...................................................................................................................17 3.5 Intake Grill..........................................................................................................................17 3.6 Chemical Dosing System ..................................................................................................18 3.7 Full Tunnel Option .............................................................................................................19

4 Outfall Structure...........................................................................................................................19 4.1 Outfall Design Overview....................................................................................................19 4.2 Outfall Location..................................................................................................................19 4.3 Outfall – Diffuser Design....................................................................................................20

4.3.1 Duckbill Performance .........................................................................................20

4.4 Outfall – Initial Dilution.......................................................................................................21

4.4.1 Initial Dilution......................................................................................................21 4.4.2 Initial Dilution under all Current Scenarios.........................................................22

4.5 Outfall – Bypass System ...................................................................................................22 4.6 Outfall – Diffuser Modifications..........................................................................................22 4.7 Outfall – Clean In Place (CIP) ...........................................................................................23

4.7.1 Process Flow......................................................................................................23

4.7.1.1 Pre-Dilution Rates Prior to the Outfall ................................................25 4.7.1.2 Dilution Achieved via Outfall...............................................................25

4.7.2 CIP – Chemicals ................................................................................................26 4.7.3 CIP Discharge Options.......................................................................................26 4.7.4 CIP - Safe Dilution Factors.................................................................................27

4.8 Outfall – Modelling.............................................................................................................28

4.8.1 Near Field...........................................................................................................28 4.8.2 Mid Field - Three-Dimensional...........................................................................28 4.8.3 Far Field - Two-Dimensional..............................................................................34

4.9 Outfall – Ecotoxicity ...........................................................................................................34

4.9.1 Ecotoxicity Assessment .....................................................................................34

4.9.2 Ecological Assessment ......................................................................................34 4.9.2.1 Marine Habitat in the Region of the Diffuser.......................................35 4.9.2.2 Salinity Tolerance of Marine Organisms.............................................35

4.9.3 Potential Impact of Outfall Discharge.................................................................37

5 Conclusions .................................................................................................................................38

5.1 Proposed Operational Monitoring......................................................................................39

6 References...................................................................................................................................40

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Appendices

Appendix A

Water Technology 2009 “Adelaide Desalination Plant - Outfall Dilution Modeling Assessment” November 2009

Appendix B

Water Technology 2009 “Adelaide Desalination Plant - Duckbill Valve Hydraulic and DilutionPerformance Investigations” October 2009

Appendix C

Clean-In-Place (CIP) Ecotoxicity Assessment Report

Appendix D

AdelaideAqua 2009 “Outfall Infrastructure Diffuser Extension – Concept Paper” November

2009 Appendix E

Table 3.1 ADP EIS (SA Water 2008)

Figures and Tables

Figure 1: Intake Structure Diagram .....................................................................................................16

Figure 3: Intake Grill Diagram .............................................................................................................18

Figure 4: General Design Arrangement for Outfall System.................................................................19

Figure 5: General Design Arrangement for Diffuser Head..................................................................20

Figure 6: Plant Production Capacity Illustrating Achievement of Initial Dilution and Augmentation with Bypass Flow. .........................................................................................22

Figure 7: Simplified Process Flow Diagram for Clean in Place Systems............................................23

Figure 8: Average Monthly Salinity Concentrations off the Coast of Port Stanvac. Error BarsRepresent Standard Deviation (Kildea et al)........................................................................29

Figure 9: Maximum Salinity Variation with Change in Ambient Salinity Levels Over a CalendarYear......................................................................................................................................30

Figure 10: Percentage Exceedance of 0.3ppt Salinity Isopleths at the Bed Relative toSubstratum Type..................................................................................................................31



Figure 13: Marine Habitats Off the Coast of Port Stanvac as Identified by DEH (2008). Waterquality sampling points (A-D) and Acoustic Doppler Current Profiler (ADCP,represented as a star) locations are included with bathymetry............................................35

Figure 14: Comparison of Average Salinity at Port Stanvac with Predicted Salinity Levels fromMid Field Model and Ecotoxicity Protective Salinity Concentration .....................................37

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Table 1: Intake and Outfall Conditions of Development Authorisation................................................10

Table 2: Intake and Outfall Conditions of the ADP Environmental Impact Statement 2008 ...............12

Table 3: Approximate volume of UF CIP solution generated per day .................................................24

Table 4: Approximate volume of RO CIP solution generated per day.................................................25

Table 5: Pre dilution rates achieved during discharged of neutralised CIP solutions .........................25

Table 6: Effective dilution rates of neutralised CIP solutions ..............................................................25

Table 7: Chemical Compositions of Neutralised CIP Samples Assessed for Ecotoxicity. ..................26

Table 8: Observed toxicity and safe dilution factors for the neutralised CIP samples ........................27

Table 9: Maximum Salinity Levels Above Ambient at 100m and 400m from the Diffuser, Time Averaged Over 1, 6 and 24 Hour Periods .............................................................................29

Table 10: Exceedance Levels at 100m and 400m for a Series of Salinity Level Increases above Ambient..................................................................................................................................30

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GLOSSARY

Term Description

ADP Adelaide Desalination Plant

Ambient Natural regional salinity levels

ANZECC Australian and New Zealand Environment and Conservation Council

ARMCANZ Agriculture and Resource Management Council of Australia and New

Zealand

Benthic Community A community of organisms living in or on the seabed.

Biofouling The overgrowth or algae, marine invertebrates, and other organisms on

nets, intake pipes, and structures in the water.

Clean In Place (CIP) The general term for the in situ cleaning of the reverse osmosis and

ultrafiltration membranes and process based equipment.

DAC South Australian Development Assessment Commission

Diffuser An engineered structure designed to release the flow of saline concentrate

into the receiving seawater with sufficient velocity and momentum to mix and

disperse the brine rapidly and effectively.

Dodge Local South Australian term for a neap tide with minimal rise and fall

generally over the course of 24-48 hours.

Ecotoxicity A study of the harmful effects of chemical compounds on species,

population and the natural environment.

EDTA / SDS Ethylenediaminetetraacetic acid / sodium dodecyl sulfate

EIS Environmental Impact Statement

Far Field Whole of Gulf St Vincent

GSV Gulf St Vincent

Hydrodynamic

modelling

A computer model that simulates the water movements, speeds, densities,

temperatures and the effects of tidal and wind influences, used to predict

salinity movement and dispersion through the receiving seawater.

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Term Description

IC10 The concentration that inhibits an endpoint by 10 %. It represents a point

estimate of a concentration of test material that causes a designated percent

inhibition (p) compared to the control. The IC10 is usually expressed as atime-dependent value, e.g. 24-hour IC10 is the concentration estimated to

cause an effect on 10% of the test organisms after 24 hours of exposure.

Initial Dilution Impact point dilution at the seabed as defined by the Roberts equation,

without consideration of salinity dispersion effects over time.

Intake System Means the infrastructure which conveys fresh seawater to the process plant.

Comprises the Intake Structure, Intake Conduit, Intake Pumping Station and

Intake Pipeline.

Intertidal Reef Zone The area between the high and low water mark of a spring tide. It is definedas the rocky platform, approximately 100m in width running along the

section of coastline adjacent to the Port Stanvac oil refinery.

Mid Benthic Zone The marine area between the depths of 12 and 18 metres that is broadly

defined by large areas of bare sand

Mid Field Greater than 100 m but less than 10km from the outfall diffuser

Minister’s Conditions

of Approval

In approving a major project, the Minister for Planning sets conditions that

must be complied with in the design, construction and operational phases of

a project. These conditions are set out in the South Australian Government

Gazette. The final authorisation for the Adelaide Desalination Plant and

conditions of approval was set out in the Gazette on 12 March 2009.

MSL Mean Sea Level

Near Field Within 100m from the outfall diffuser.

NOEC The highest observed concentration of a toxicant used in a toxicity test that

does not exert a statistically significant adverse effect (P > 0.05) on the

exposed population of test organisms compared to the controls. This is

estimated by hypothesis based statistical methods and is therefore not a

point estimate.

Outfall System Means the infrastructure which conveys Saline Concentrate from the

Process Plant through the Outfall Conduit to the Sea. Comprises the outfall

shaft, outfall tunnel, riser shafts and diffuser system.

PLC Program Logic Controller

Protective

concentrations (PC)

The concentration predicted by species sensitivity distribution methods that

will protect a chosen percentage of species from experiencing toxic effects.

For example, the PC99 should protect 99% of species in the ecosystem

being considered.

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Term Description

ppt Parts per thousand, expressed as a mass unit as grams of solute (e.g. salt)

in kilograms of solution

Roberts’ Equations A set of experimentally derived design formulae that represent best practise

design formulae for predictions of impact point dilution of inclined dense jets

into stationary environments.

RO Permeate Desalinated water from RO membranes that has not been dosed with any

post-treatment chemicals.

Safe dilution factors The concentration that a chemical or discharge must be diluted by in order

to meet a selected PC value. The lower the PC value the higher the dilution

factor must be to protect the selected percentage of species.

Saline Concentrate A liquid by-product of the desalination process that has a higher

concentration of suspended and dissolved materials (particularly salt) than

intake seawater due to the salt concentrating effect of the reverse osmosis

system.

Subtidal Reef Zone The area defined as the medium to low profile reef that extends from the low

water mark to a depth of approximately 12 metres.

Slack Tides Period of minimal tidal movement, occurring at the turn of the tide.

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1 IntroductionThe primary purpose of the Adelaide Desalination Plant is to deliver a climate independent supply of

100 billion litres of potable water per year, to secure and diversify metropolitan Adelaide’s water

supply system and offset reduced reservoir inflows from the Mt Lofty Ranges and Murray-Darling

Basin.

The Adelaide Desalination Project was granted Major Development status by the South Australian

Government on 17 April 2008, which triggered a comprehensive and coordinated assessment

process culminating in the publication of an Environmental Impact Statement (EIS) for community

comment. The project proponent, SA Water, produced a Response document to address all

community concerns and Development Approval was granted in March 2009 by the Minister for Urban

Development and Planning. The Minister’s Conditions of Approval (gazetted Development

Authorisation Conditions) and the EIS define specific environmental conditions to be achieved in the

design, construction and operation of the plant.

The Adelaide Desalination Project design and construct contract was awarded to AdelaideAqua D&C

consortium in February 2009. Construction commenced in April 2009 and delivery of first water will be

in December 2010. It is expected that the plant will be fully operational in late 2012.

The plant is required to have a production capacity of 300ML/day. Due to variations in seawater

salinity and temperature, and depending on plant operating conditions, the plant can produce up to

326ML/day.

The plant will include the following key elements:

• A seawater intake structure and connecting tunnel/s and pipelines;

• Intake pumping station and screening system;

• Pre-treatment system and associated buildings;

• Reverse osmosis treatment system and associated buildings;

• Post-treatment system and associated buildings;

• An outfall structure with diffusers and connecting tunnel/s and pipelines;

• Waste treatment area, including solids thickening and dewatering.

In addition, the Desalination Project will include:

• Transfer pump station for pumping desalinated water to the Happy Valley Water Treatment

Plant. This pump station is not part of the Major Development assessment process and hasbeen subject to a separate assessment under Section 49 (Crown Development) of the

Development Act 1993;

• Dedicated areas for unloading and storage of chemicals associated with the Plant;

• Electrical substation, power cabling and switchgear for distributing power within the site;

• Energy recovery facility for the saline concentrate prior to its discharge to the Gulf St Vincent;

• Site access roads, internal access roads and parking areas;

• Stormwater management infrastructure and other buried services across the site;

• Site offices and administration buildings, control rooms, laboratory, research and developmenttest facility, and a visitor education/interpretive centre; and

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• Site landscaping, lighting and security fencing across the site.

One key aspect of the ADP is the requirement for the Intake and Outfall Systems to meet specified

performance criteria for design, construction and operation to ensure that environmental protection

objectives are achieved.

The Environmental Impact Statement and subsequent Response document (EIS – SA Water 2008)

presented during the Major Development Approval process for the Adelaide Desalination Plant (ADP)

was based on a concept design with specific environmental and engineering performance criteria.

The environmental and engineering performance objectives established by SA Water (EIS – SA

Water 2008 – Table 3.1) and the Minister’s Conditions of Approval (Development Authorisation

Conditions Gazetted June 2009) provide the functional requirements for AdelaideAqua D&C

Consortium (AA) detailed design.

This report summarises the technical investigations and detailed design carried out to confirm that the

performance criteria of the Intake and Outfall Systems are in compliance with the ADP EIS (SA Water

2009) and Development Authorisation Conditions (June 2009, pg 2707-2708).

The purpose of this report is to:

• Identify the legislative and contractual requirements for the intake and outfall systems of the

ADP

• Demonstrate that the specified requirements for design and performance are met

• Recognise the over-arching requirement to not “pollute the environment in a way that causes or

may cause environmental harm (DA Conditions, June 2009, pg 2708)

• Discuss the potential operational licence conditions

• Summarise and present key information contained within the various appendices

This report must be read in conjunction with the following documents included in the appendices.

• Adelaide Desalination Plant Outfall Dilution Modelling Assessment November 2009

• Adelaide Desalination Plant Duckbill Valve Hydraulic and Dilution Performance Investigations

October 2009

• Ecotoxicity Evaluation of Adelaide Desalination Plant Effluent and Process Chemicals

November 2009

• Clean-In-Place (CIP) Ecotoxicity Assessment Report Document Reference E015-020-2974

2009

• Outfall Infrastructure Diffuser Extension – Concept Paper. November 2009

• Diffuser Selection Report – December 2009

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2 Environmental Objectives and PerformanceCriteria

2.1 Conditions of Development Authorisation Gazetted 11th June 2009 (DAConditions)

Table 1: Intake and Outfall Conditions of Development Authorisation

Criteria Criteria

Achieved

Statement of

Compliance

Report Reference

Intake Structure – Condition 9

The proponent shall design, construct and operate the intake infrastructure in accordance with design

parameters provided in the Environmental Objectives and Performance Criteria (or as modified by the EPA

through licensing requirements) including the following parameters:

a) location of the intake structuremust be within the mid to deepbenthic zone (Figure 2);

Yes Location of intake

structure is within the

mid benthic zone

3.2 Intake Location

b) Intake structure to be located at asufficient distance from the subtidalreef area to minimise the risk ofentrainment or entrapment of reefspecies;

Yes intake structure is

approximately 700m

from the subtidal reef

zone

3.3 Subtidal Reef

and

Figure 2

c) seawater intake velocity at theentry to the intake structure shouldnot exceed 0.15 m/s under anyoperating condition;

Yes Maximum Intake velocitydoes not exceed

0.15m/s.

3.4 Intake Velocity

d) seawater intake to incorporatescreen/grill to restrict ingress ofmarine biota with a maximum cleargrill spacing of 75 millimetres (asinstalled); and

Yes The intake screen’s

clear grill spacing is

75mm.

3.5 Intake Grill

e) Any chlorination (or approvedbiocide) dosing system from the

intake structure must ensure thatthere is no backflow of chemicaldosing into the marineenvironment.

Yes The chemical dosing

system is located to

prevent backflow into

the marine environment.

3.6 Chemical

Dosing System

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Criteria Criteria

Achieved

Statement of

Compliance

Report Reference

In addition to the above performance

criteria, the proponent shall design theintake infrastructure as follows (or as

modified by the EPA through licensing

requirements):

f) Installation of the full tunnel option(and not the hybrid tunnel option)for the intake and outfallinfrastructure.

Yes Both intake and outfall

systems are full tunnels.

3.7 Full Tunnel

Option

Outfall Structure – Condition 10

The proponent shall design, construct and operate the outfall infrastructure in accordance with design

parameters provided in the Environmental Objectives and Performance Criteria (or as modified by the EPAthrough licensing requirements) including the following parameters:

a) location of the outfall structuremust be positioned within theenvelope zone shown in Figure 2 and far enough from the intake toavoid any short circuiting;

Yes Outfall structure located

within designated

envelope, and distance

from intake sufficient to

avoid short circuiting.

4.2 Outfall Location

b) the outfall system must terminatewith diffusers designed to promote

rapid dispersion of the salineconcentrate into the surroundingseawater;

Yes Duckbill valves have

been utilised to promote

rapid dispersion of

saline concentrate.

4.3 Outfall –

Diffuser Design

c) the outfall must achieve therequired initial dilution of 50:1 atthe seabed, under all currentscenarios for the full range ofoperating conditions/flows;

Yes Design achieves initial

dilution of at least 58:1

under all current and

plant flow scenarios to

account for the higher

process recovery rate.

4.4 Outfall – Initial

Dilution

d) the design of the outfall system

should include consideration of theuse of bypass flows or othermeasures to ensure theachievement of the target dilutionrequirements, particularly underlow discharge flows;

Yes Bypass system is

provided to ensure initial

dilution achieved during

low discharge flows.

4.5 Outfall –

Bypass System

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Criteria Criteria

Achieved

Statement of

Compliance

Report Reference

e) the outfall diffuser shall be capable

of:o being extended; and

o being modified to reduce thenumber of diffuser outletsand/or to adjust dispersion ratesfrom each diffuser outlet; and

Yes Outfall diffuser system

has been designed to becapable of being

extended and modified

to adjust dispersion

rates from each diffuser

outlet.

4.6 Outfall –

DiffuserModifications

f) The saline concentrate dischargemust not contain Cleaning in Place(CIP) chemicals or any otherpreservation chemicals, unlesspermitted by the EPA through

licensing requirements.

Yes Discharge of CIP via the

outfall will only be

incorporated if permitted

by the EPA

4.7 Outfall – Clean

In Place (CIP)

2.2 ADP Environmental Impact Statement (EIS)

The Intake and Outfall Systems Environmental Objectives and Performance Criteria prescribed in

Table 3.1 ADP EIS and Response document (SA Water 2008) (Appendix 5) is summarised below:

Table 2: Intake and Outfall Conditions of the ADP Environmental Impact Statement 2008

Criteria Criteria Achieved Statement of

Compliance

Report Reference

Intake Structure

Design and operation to ensure:

a) Location of the intakestructure must be withinthe mid benthic zone(Figure 2).

Yes Location of intake

structure is within the

mid benthic zone

3.1 Intake Design

Overview

3.2 Intake Location

b) Intake structure to belocated at a sufficient

distance from thesubtidal reef area tominimise the risk ofentrainment orentrapment of reefspecies.

Yes Intake structure is

approximately 700m

from the subtidal reef

zone

3.2 Intake Location

3.3 Subtidal Reef

c) Location of theseawater intakestructure at a heightabove the seabed tominimise the risk ofentrainment of sediment

or floating debris.

Yes Intake structure

located 8m above the

seabed, and 12m

below mean sea level.

3.2 Intake Location

Figure 1

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Compliance

Report Reference

d) Seawater intake velocity

at the entry to the intakestructure should notexceed 0.15m/s underany operating condition

Yes Maximum Intake

velocity does notexceed 0.15m/s

3.4 Intake Velocity

e) Seawater intake toincorporate screen/grillto restrict ingress ofmarine biota with amaximum clear grillspacing of 75millimetres (asinstalled).

Yes The intake screen’s

clear grill spacing is

75mm.

3.5 Intake Grill

f) Any chlorination (orapproved biocide)dosing system from theintake structure mustensure that there is nobackflow of chemicaldosing into the marineenvironment.

Yes The chemical dosing

system is located to

prevent backflow into

the marine

environment.

3.6 Chemical Dosing

System

g) Develop and implementa monitoring program(as part of the

OperationalEnvironmentManagement andMonitoring Plan) inaccordance with MajorDevelopment approvaland EPA licence,including:

o Monitoring andreporting onentrainment on marinebiota.

Yes.

Under development

Operational

Management and

Monitoring Program

will be developed in

accordance with

license conditions for

plant operation and

maintenance phase

5.1 Proposed Operational

Monitoring

Outfall Structure

The saline concentrate discharge must comply with EPA licence conditions and any other regulatory

requirements.

Design and operation to ensure:

a) The outfall structuremust be positionedwithin the envelopezone shown in Figure 2 and far enough from theintake to avoid any

short circuiting.

Yes Outfall structure

located within

designated envelope,

and distance from

intake sufficient to

avoid short circuiting

4.1 Outfall Design

Overview


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Compliance

Report Reference

b) The outfall system must

terminate with diffusersdesigned to promoterapid dispersion of thesaline concentrate intothe surroundingseawater.

Yes Duckbill valves have

been utilised to promote rapid

dispersion of saline

concentrate

4.3 Outfall – Diffuser

Design

c) The outfall mustachieve the requiredinitial dilution of 50:1 atthe seabed, or asotherwise agreed withthe EPA, under all

current scenarios for thefull range of operatingconditions / flows.

Yes Design achieves initial

dilution of at least 58:1

under all current and

plant flow scenarios to

account for the higher

process recovery rate.

4.4 Outfall – Initial Dilution

d) The design of the outfallsystem should includeconsideration of the useof bypass flows or othermeasures to ensure theachievement of thetarget dilutionrequirements,particularly under low

discharge flows.

Yes Bypass system is

provided to ensure

initial dilution achieved

during low discharge

flows.

4.5 Outfall – Bypass

System

e) The outfall diffuser shallbe capable of:

o being extended; and

o being modified toreduce the number ofdiffuser outlets and/orto adjust dispersionrates from eachdiffuser outlet.

Yes Outfall diffuser system

has been designed to

be capable of being

extended and modified

to adjust dispersion

rates from each

diffuser outlet

4.6 Outfall – Diffuser

Modifications

f) The saline concentratedischarge must notcontain Cleaning inPlace (CIP) chemicalsor any otherpreservation chemicals,unless permitted by theregulatory authorities.

Yes Discharge of CIP via

the outfall will only be

incorporated if

permitted by the EPA

4.7 Outfall – Clean In

Place (CIP)

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Each of the above conditions for the Intake and Outfall Systems are addressed in the followingsections.

3 Intake Structure

3.1 Intake Design Overview

The intake riser will be connected into the intake tunnel which extends 1.4km from the tunnel shaft

onshore, to bring seawater into the desalination plant. The riser shaft extends vertically 20m from the

tunnel, and is connected to the intake structure head at the seabed. The intake structure head

extends approximately 8m above the seabed and is 12m below mean seawater level (MSL). The

design of the Marine Intake Head structure incorporates (refer to Figure 1):

• A base stem or shaft of 5.4m internal diameter that encompasses the Intake Riser. This section

of the intake structure is located below the seabed;

• A 9.5m internal diameter seawater intake head sits on the base stem. The cylindrical head

structure has eight equal openings through which seawater is drawn in;

• The eight equal openings are covered with a cupronickel grill structure having 75mm clear

spacing between the grills. The presence of these grills on the intake head are intended to

minimise the ingress of marine fauna; and

• The intake structure is surrounded by rock armour to prevent erosion of the seabed around the

intake head and to provide additional support and protection to the base stem.

Figure 1: Intake Structure Diagram

3.2 Intake Location

The intake structure is located 1.2km offshore, within the mid benthic zone (Figure 2) and themarine exclusion zone defined in the Notice to Mariners No. 43 of 2009.

Riser

Zone

Marine

Zone

0.15m/s

0.8m/s

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The cupronickel inhibits marine growth on the grill. Cupronickel is commonly used in marine

applications on pipes, offshore platforms and inside condensors to reduce biofouling. Latest research

into the mechanism by which the cupronickel prevents marine growth is that a protective surface

oxide film forms naturally in seawater to discourage biofouling (Powell 2004).

Figure 3: Intake Grill Diagram

3.6 Chemical Dosing System

A chemical dosing system is used to treat incoming seawater to prevent fouling of the intake tunnel as

a result of marine growth. Chlorine dosing generally occurs daily for 20 minutes to 1 hour duration.

Seawater chlorinated as a result of the tunnel cleaning process is de-chlorinated within the plant. The

design of the intake structure and dosing system ensures that no chemicals are released to the

marine environment at the intake through incorporation of the following:

• Control interlocks preventing dosing of the chemicals to the intake tunnel if the intake pump

station is not operational

• Control interlocks to immediately stop chemical dosing if the intake pumping station stops

• Flushing of the chemical dosing lines after each use to prevent any residual chemicals

remaining within the dosing system

• Locating the chemical dosing system sparge ring, approximately 8m below the underside of the

intake bar screens

• Provision of a surge chamber within the intake pumping station to store any upsurge of water

from the intake tunnel in the event of an emergency pump station stop.

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• Approximately 180m3 of storage within the intake structure, below the inlet screen, is available

to contain any surge event, thereby preventing the release of chemicals during an emergency

pump station stop. A surge analysis of the worst case scenario (emergency stop of fully

operating pumping system) has been conducted to demonstrate that there is sufficient capacity

within the confines of the tunnel and intake system to contain the chemically treated intakewater during this transient event.

3.7 Full Tunnel Option

The intake and outfall systems consist of full length tunnels terminating in the mid to deep benthic

zones.

4 Outfall Structure

4.1 Outfall Design Overview

The outfall system is gravity operated and designed to facilitate the effective dispersion of the salineconcentrate produced during the desalination process. A tunnel beneath the seabed conveys the

saline concentrate offshore to six separate risers located along the last section of the outfall tunnel

with the outermost riser being located approximately 850m offshore. Each riser is approximately 20m

long and connects the outfall tunnel to the diffuser heads on the seabed. The diffuser heads

incorporate duckbill valves designed to disperse the saline concentrate into the seawater. The duckbill

valves themselves are raised off the seabed, at a water depth of approximately 16.5 m at MSL.

The general arrangement of the outfall structure is illustrated in Figure 4.

Figure 4: General Design Arrangement for Outfall System


The outfall diffuser is located to the east of the intake to assist with the dispersal of the diluted saline

concentrate away from the diffuser through the gravity action of the seabed slope acting in

conjunction with tidal and local wind-driven coastal currents. Positioning the outfall diffuser in this

location takes advantage of the hydrodynamics in the area and assists in the midfield advection and

diffusion of the diluted saline concentrate stream.

The outfall design:

• Achieves rapid dispersion of the saline concentrate with the surrounding sea water

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• Ensures the diffuser is located well away from and does not have any effect upon sensitive

habitats such as reefs

• Locates the diffuser appropriately to avoid short circuiting of the outfall saline concentrate into

the intake structure

• Minimises interference of adjacent discharge plumes

• Provides improved dispersion of the diluted saline concentrate under low current conditions

when the main flushing mechanism is gravity driven, as the plume flows down the natural slope

of the sea bed.

The location of the Outfall structure is shown in Figure 2 above.

4.3 Outfall – Diffuser Design

The outfall diffuser arrangement consists of 24 x 250mm duckbill diffuser ports, arranged in groups of

four duckbill valves on each of the six diffuser heads mounted on a line of six risers which will be

connected directly to the outfall tunnel, under the seabed. The distance from inshore to offshorediffuser head will be 140m.

Figure 5: General Design Arrangement for Diffuser Head

This configuration was one of several considered, and was selected due to its optimal dilution

performance whilst still satisfying outfall tunnel pressure constraints. Further information on the

process for selection of the diffuser system is provided in the Diffuser Selection Report (Appendix 6).

4.3.1 Duckbil l Performance

Duckbill valves are commonly used on marine discharge systems and have been assessed for their

suitability and durability in this application.

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Long term performance of the diffuser system is reliant upon the elasticity and stiffness of the duckbill

valves. This will be examined through a regular monitoring program in order to fully document the

behaviour of the valves over time in this particular environment. However, experience to date

indicates that significant stiffness or elasticity degradation should not occur over the short or medium

term and therefore should not affect performance. The potential for total failure of a duckbill valve,

while considered unlikely, has been considered in the design of the outfall system by providing a

flange connection to allow easy replacement of the valve if required.

A sensitivity analysis was undertaken on performance of the outfall system with the loss of two

duckbill valves, which indicates that the performance of the outfall as a whole is not significantly

impacted. Loss of valves will be detectable through trend analysis of the water levels in the outfall

shaft, or through inspections. Subtle losses in stiffness of valves, and corresponding impact to diffuser

performance, will be detected through the regular inspection program.

4.4 Outfall – Initial Dilution

The EIS calls for an initial dilution of 50:1 which was based on a nominal recovery rate of 45%. As the

ADP will be designed for a recovery rate of up to 48.5%, the equivalent initial dilution has been taken

as 58:1 to reflect the higher recovery. This is in accordance with discussions with the EPA.

4.4.1 Initial Dilution

Initial dilution is defined as impact point dilution at the seabed as calculated by the Roberts equation

(Roberts et al 1997).

The empirical relations as developed by Roberts et al (1997) have been widely applied to diffuser

design and near field mixing analysis and dispersion of dense plumes, and are considered current

best practice to determine initial dilution ratios.

It should be noted that the Roberts equation does not consider the effects of salinity dispersion overtime. This has been considered through mid field hydrodynamic modelling, and assessed against the

results of the ecotoxicity analysis. This ensures maximum salinity levels as predicted by the

hydrodynamic model are considered when assessing potential environmental impact.

Extensive physical modelling and prototype testing of the duckbill valves was undertaken as part of

the detailed design of the outfall diffuser (Appendix 2). These investigations were undertaken to

evaluate the capability of duckbill valves to develop appropriate hydraulic conditions at the diffuser

ports and thereby maintain adequate initial dilutions over the full range of outfall flow rates. The

physical model successfully demonstrated that the Duckbill dilution performance maintains high

velocities under low flows, as well as enhanced mixing due to the elliptical shape of the duckbill jets.

The predicted initial dilution at various plant productions is presented in Figure 6 below. Note thatduring periods of less than 39% plant production the required initial dilution is maintained by

augmenting the flow by pumping seawater through the bypass system (refer to Section 4.5).

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Figure 6: Plant Production Capacity Illustrating Achievement of Initial Dilution and Augmentation with

Bypass Flow.

These dilution calculations were based on the Roberts model (Water Technology 2009b), and were

validated in a laboratory using scaled diffuser ports in large water tanks (Appendix 1).

4.4.2 Initial Dilution under all Current Scenarios

Dilution is significantly enhanced by the actions of winds, tidal movements and cross currents. Even

during slack or dodge tides, some cross current effects and / or wind will be evident.

Despite these likely contributions, initial dilution rates have been calculated assuming zerocontribution from the effects of wind and / or cross currents. That is, the design calculates initial

dilution ratios on the basis that the receiving waters are stationary.

The existence of cross currents at the outfall will increase dilution of the diffuser plumes such that the

net impact of any cross currents will be to increase dilution above that calculated under quiescent

conditions.

4.5 Outfall – Bypass System

For plant production rates below 39% of full capacity, a bypass flow will be incorporated to ensure that

the minimum criterion of 58:1 is achieved.

The current proposal for the bypass system is to dilute the saline concentrate by piping seawater from

within the RO plant into the saline concentrate discharge system. As the RO plant can only operate

and discharge saline concentrate when there is seawater coming into the plant through this line, there

will always be seawater available to dilute the saline concentrate when it is discharged. The PLC will

be programmed to open the valves and introduce dilution water based on actual plant flow.

An opportunity exists to take advantage of natural tidal and current movements and utilises the

bypass system during dodge tide events only. This approach results in reduced power consumption

and is the preferred option.

4.6 Outfall – Diffuser Modifications

The Outfall Infrastructure Diffuser Extension – Concept Paper, Nov 2009 (Appendix 4) details the

proposed design for extending the diffuser. The concept design allows for a number of diffuser

Bypass

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options (Appendix 4). All options utilise the existing infrastructure with a bolted connection to the top

of the risers. The concept design indicates the outfall hydraulics is feasible, and flow rates through

the 900mm diameter outfall pipe would not significantly change the hydraulic losses through the

extended system.

4.7 Outfall – Clean In Place (CIP)

Clean in Place (CIP) is the general term for in situ cleaning of the Reverse Osmosis (RO) and

Ultrafiltration (UF) membranes. Cleaning of the membranes is required to remove any scaling, or

fouling observed during the long term operation of the plant.

4.7.1 Process Flow

Seawater is pre-treated using a submerged type UF membrane system. Pre-treatment ensures the

seawater is of suitable quality to prevent RO membrane damage. Backwashing and cleaning of the

UF system is required to remove any solids collected and maintain system performance accordingly.

UF filtrate is pumped into the first pass RO racks at high pressure (approximately 70 bar). The firstpass RO system produces permeate (low salinity product water) at a 50% recovery ratio with the

remaining 50% (saline concentrate) passing through energy recovery devices to minimise power

consumption. Product water is re-treated through second pass RO racks to ensure the quality of the

permeate meets Australian Drinking Water Quality guidelines. Permeate water from the RO plant is

then re-mineralised disinfected and fluoridated before distribution.

The CIP system proposed is summarised in the outline process flow diagram in Figure 7.

Figure 7: Simplified Process Flow Diagram for Clean in Place Systems

The UF system will gradually foul due to solids build-up during operation. Regular backwashing and

air scrubbing will be used to dislodge solids. Backwash water is then transferred to the Wash Water

Treatment Facility for further treatment and is not the subject of this report. After a period of time

backwashing operations alone will not clean the membranes satisfactorily and chemical cleaning willbe required to maintain performance.

Reverse Osmosis

Rack(s)

800kL Holding

Tank

RO CIP

Recirculation

Tank (75kL)

RO CIP Neutralisation

Tank (75kL)

Chemical Building

CIP Solution Preparation

UF CIPRecirculation

System

UF CIP Neutralisation

Tank (185kL)To Outfall

System

Neutralisation

Capability

Water QualityMonitoring

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Membranes racks / tanks are taken offline and are cleaned based on plant configuration, to maintain

production with the remaining operational membranes. Each CIP cycle may involve multiple batches

of chemicals to achieve the required clean. Once complete, each batch is directed to a neutralisation

tank to neutralise the chemical.

Most chemicals used during CIP are either acids or alkalines, and when neutralised generate a saltbased solution (> 4,000mg/L on average). Neutralised CIP solutions have been assessed to

determine a safe dilution factor to determine suitability for potential discharge, subject to EPA

approval.

Operational ultra filtration cells will be cleaned on a time basis using a dedicated clean in place

system as follows.

• Maintenance Cleaning – Every 2 days using 42 kL of a solution of sodium hypochlorite (0.3 g

Cl2/L) and every 4 days using 42 kL of a solution of sulphuric acid (1g/L)

• Recovery Cleaning – Every 30 days using 42 kL of a solution of sulphuric acid (1g/L) and citric

acid (2.5g/L) followed (in a different batch process to avoid contact) by 42 kL of a solution of

sodium hypochlorite (1.0 g Cl2/L). The order of these chemicals may be reversed.

Table 3 summarises the approximate volume of UF CIP solution generated per day. Should the

desalination plant be operating at less than full capacity the volume of CIP solution discharged will

decrease in proportion to the reduction in product water capacity, i.e. 50% production capacity = 50%

UF CIP volume.

Table 3: Approximate volume of UF CIP solution generated per day

Cycle Number o fUF Cells

Frequency Volume perClean (kL)(includingflushing)

Average No. ofCells Cleaned perDay

AverageVolume per Day(kL)

Maintenance

Cleaning NaClO

28 Every 2 days 185 14 2,590

Maintenance

Cleaning

H2SO4

28 Every 4 days 185 7 1,295

Recovery

Cleaning NaClO

/ H2SO4 + citric

acid

28 Every 30 days 370 1 370

Periodic cleaning of the RO membranes is also necessary to maintain the plant performance by

removing scaling and potential foulants. The cleaning frequency depends on the raw water conditions,

efficiency of the pre-treatment system and operational conditions of the system. The membranes are

cleaned in place by recirculating cleaning solutions through the pressure vessels in each RO rack.

Different cleaning protocols can be used to specifically address each type of fouling by varying the

type of chemical, concentration, pH, temperature and cleaning duration.

Table 4 summarises the approximate average volume of RO CIP solution generated per day. RO CIP

is conducted on a performance basis and not strictly a time basis as summarised below. Therefore,

the average cleaning frequency in Table 4 is considered the worst case scenario resulting in the

largest volume of cleaning solution. Operators at the desalination plant will aim to minimise the

frequency of cleaning in line with plant performance.

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Table 4: Approximate volume of RO CIP solution generated per day

Cycle Number ofRO trains

Frequency Volume perClean (kL)(includingflushing)

Average No. ofRacks Cleaned perDay

Average Volumeper Day (kL)

1st Pass 20 Every 14 days 300 1.4 420

2nd Pass 10 Every 2 months 300 0.2 60

4.7.1.1 Pre-Dilution Rates Prior to the Outfall

The following pre-dilution rates are achieved during the discharge of neutralised CIP solution under

high and low desalination plant production scenarios. Pre-dilution is deemed to be the dilution

achieved in the gravity outfall pipes, shaft and tunnel prior to release via the outfall diffusers.

Effective pre-dilution rates between 3:1 and 16:1 are achieved in the outfall system prior to release

when neutralised CIP solutions are discharged at the maximum design flow rate.

Table 5: Pre dilution rates achieved during discharged of neutralised CIP solutions

Plant Production 30ML/d Plant Product ion 300ML/day

Area

MaximumCIP Flow(L/s)

OutfallFlow (L/s)

Pre-dilution priorto diffusers

(outfall : CIP)

MaximumCIP Flow(L/s)

OutfallFlow (L/s)

Pre-dilution prio rto diffusers

outfall: CIP)

UF CIP 175 525 3:1 700 4200 6:1

RO CIP 60 410 7:1 240 3740 16:1

4.7.1.2 Dilut ion Achieved via Outfall

Dilution rates achieved for neutralised CIP solutions need to consider the initial dilution achieved via

the outfall diffusers, combined with the predilution which occurs when neutralised CIP is mixed into

the saline concentrate prior to discharge.

Table 6: Effective dilution rates of neutralised CIP solutions

Plant Production 30ML/d Plant Product ion 300ML/day

Area

Pre-dilutionprior to

diffusers(outfall:CIP)

InitialDilution viaOutfall

(seawater:outfall)

Effective CIP

Dilution(seawater:CIP)

Pre-dilutionprior to

diffusers(outfall:CIP)

Initial Dilutionvia Outfall

(seawater:outfall)

Effective CIP

Dilution(seawater:CIP)

UF CIP 3:1 58:1 174:1 6:1 81:1 486:1

RO CIP 7:1 58:1 406:1 16:1 81:1 1296:1

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4.7.2 CIP – Chemicals

An ecotoxicity assessment was undertaken of the neutralised CIP chemicals in order to determine

those chemicals likely to pose an environmental impact if discharged. The chemical compositions of

these solutions were subjected to further lab based testing, and are defined in Table 7.

Table 7: Chemical Compositions of Neutralised CIP Samples Assessed for Ecotoxicity.

Sample

No.Description Solute Chemical Concentration Neutralization

1.Saline Concentrate -

Control

Saline

concentrateNo chemicals Nil Nil

2.

Saline Concentrate

following chlorination /

dechlorination

Saline

Concentrate

Sodium

hypochlorite

15 mg/l (as Cl2)

free chlorine

Neutralised with sodium

metabisulphite until free

chlorine disappear

Sulphuric acid 1,000 mg/l

3. Neutralised UF CIPSolutionROPermeate

Citric acid 2,500 mg/l

Neutralised with causticsoda

4.Neutralised RO CIP

Solution

RO

Permeate

DBNPA

solution30 mg/l

Neutralised with sodium

metabisulphite

Sodium

hydroxide

0.13% w/w until

pH 12.5

Sodium

dodecyl

sulphate

0.05% w/w5.

Neutralised RO CIP

Solution B

RO

Permeate

Na4-EDTA 0.35% w/w

Neutralised with sulphuric

acid

6.Polyelectrolyte

FlocculantSeawater Polymer LT25 0.1% w/w Nil

The ADP will also apply antiscalants to prevent RO membrane scaling. The ecotoxicity studies for

various antiscalants have been previously presented to EPA by SA Water as part of the EIS

submission. The safe dilution factors for antiscalants are provided in Appendix 4.

4.7.3 CIP Discharge Options

The discharge options for neutralised CIP chemicals are:

Trade Waste

This was considered but was eliminated for the majority of chemicals as the receiving treatment

system (i.e. municipal wastewater treatment plants) is unable to accept the high flowrates, volumes

and salinity levels. Average salinity of neutralised CIP solutions exceeds trade waste discharge limit

of 1,400mg/L and would restrict future reuse opportunities from Christies Beach WWTW. Note that it

is proposed to discharge the EDTA / sodium dodecyl sulphate (SDS) solution to trade waste, as this is

considered potentially harmful to the marine environment without further treatment.

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Onsite Treatment

Onsite treatment through further concentration is possible, but is energy and chemically intensive, and

generates large volumes of waste solutions that would require road transport to prescribed waste

landfill sites.

Outfall Discharge

Discharge of neutralised CIP saline streams into the marine environment through the outfall diffuser

system is considered standard industry practice nationally and worldwide. Ecotoxicity assessment has

been performed to determine safe dilution levels and ensure that the design of the outfall system will

achieve the required dilution required to prevent environmental harm.

This has been undertaken, and the resultant safe dilution levels are summarised below.

4.7.4 CIP - Safe Dilu tion Factors

Safe dilution factors of the neutralised CIP samples were determined through the ecotoxicity testing

(Appendix 3) to evaluate risk of environmental harm. The observed toxicity and safe dilution factorsfor the neutralised CIP samples are described in Table 8.

Table 8: Observed toxicity and safe dilution factors for the neutralised CIP samples

Sample

No.Description

Safe Dilution Factor

(protect 95% of species)

Minimum

Dilution

achieved

Maximum

Dilution AchievedProposed

Discharge

1.

Saline

Concentrate -

Control

20:1

58:1 81:1

Outfall

2.

Saline

Concentrate

following

chlorination /

dechlorination

21:1

58:1 81:1

Outfall

3.Neutralised UF

CIP Solution21:1

174:11 486:1Outfall

4.Neutralised RO

CIP Solution11:1

406:1 1296:1Outfall

5.

Neutralised RO

CIP Solution

(EDTA / SDS)

2500:1

406:1 1296:1

Trade Waste

6.Polyelectrolyte

Flocculent10:1

58:1 81:1Outfall

The results of the ecotoxicity testing conclude:

• A toxicity response was observed in all saline concentrate, permeate and feedwater samples;

• The majority of the observed toxicity in the saline concentrate is believed to have been caused

by the salinity of the samples; and

• The diffusion that is achieved by the diffuser dilution (Refer to Section 4.7.1.1) adequately

achieves the safe dilution for five of the samples tested.

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• Sample 5 - Neutralised RO CIP Solution (EDTA/SDS) is unable to be discharged safely into the

Marine environment, therefore this waste stream will be disposed of via trade waste.

4.8 Outfall – Modelling

The hydrodynamic assessment (Appendix 1) of the outfall diffuser has been undertaken at thefollowing three different spatial scales:

• Near-field modelling of the individual saline concentrate diffuser plumes

• Three-dimensional, mid-field numerical modelling of the outfall diffuser and coastal waters at

Port Stanvac

• Two-dimensional, far-field numerical modelling for the hydrodynamics of the Whole of Gulf St.

Vincent

It should be noted that reference to 120% plant flow shown within the Outfall Dilution Modelling

assessment is included for purposes of clarity of the relevant graphs only. This is not intended to

reflect a likely operating condition.

4.8.1 Near Field

Near field modelling was conducted to determine initial dilution ratios achieved by the outfall diffusers,

and has been addressed in Appendix 1 and summarised in Section 4.4.

4.8.2 Mid Field - Three-Dimensional

The mid field model examines a number of different scenarios to determine the influence of currents,

wind patterns and tidal conditions on the behaviour of the saline concentrate discharged from the

diffuser. The model is a three dimensional mathematical representation of the receiving environment

around the diffusers and is used to predict the variation of salinity over space and time. The modelconsiders an area of 20km by 11.5km.around at the diffusers at Port Stanvac. The model has been

reviewed to ensure accuracy particularly at points 100m and further from the diffusers. The model

considers potential build-up of a dense saline layer at the seabed in the vicinity of the diffusers, and

the impact of this layer being re-entrained into the diffuser jets.

Three representative tidal and meteorological scenarios have been assessed and are considered to

capture the envelope of conditions that would influence the dilution performance of the outfall diffuser.

The scenarios are:

• Scenario 1 - Six week scenario from 1 May to 15 June 2006

• Scenario 2 – A worst case dodge tide scenario

• Scenario 3 – A scenario containing an upwelling (onshore advection) of bottom waters

A detailed analysis of each of the scenarios is provided in Appendix 1.

The data generated by the midfield model assumes continuous plant operation at 100% capacity and

48.5 % recovery.

Ambient salinity concentrations were measured over a 12 month period and vary from 36 ppt during

spring to 38 ppt around early autumn. This broad salinity range is characteristic of the upper and mid

regions of Gulf of St Vincent. Further south the Gulf waters are influenced more by oceanic conditions

and as a result ambient salinity concentrations tend to be lower and more constant. Figure 8

illustrates average monthly salinity concentrations off the coast of Port Stanvac for 2008-2009.

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Note; This dataset covers a twelve month period, however the salinity of the seawater in the Gulf of St

Vincent may fluctuate more than this due to natural variability. As a result, the plant itself has been

designed to treat intake seawater up to a maximum of 42g/L salinity.

Figure 8: Average Monthly Salinity Concentrations off the Coast of Port Stanvac. Error Bars Represent

Standard Deviation (Kildea et al)

The results of the model can be used to predict salinity levels over time at any point within the model

area, relative to regional ambient salinity concentrations. These results show that the maximum

salinity that will occur at 100m and 400m from the diffuser averaged over 1, 6 and 24 hour periods is

as follows:

Table 9: Maximum Salinity Levels Above Ambient at 100m and 400m from the Diffuser, Time Averaged

Over 1, 6 and 24 Hour Periods

Max Salinity at 100m (ppt) Max Salinity at 400m (ppt)

Time average (hr) Onshore Offshore Onshore Offshore

1 hr 0.8 1.0 0.2 0.7

6 hr 0.6 0.9 0.2 0.6

24 hr 0.4 0.8 0.2 0.5

This information can be further expressed as maximum predicted variation to annual ambient salinity

and is demonstrated in Figure 9 below:

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Figure 9: Maximum Salinity Variation with Change in Ambient Salinity Levels Over a Calendar Year

Significant variations to ambient salinity generally occur for short periods of time only, and the model

is able to predict the amount of time that these salinity variations occur. Model results for the 6 week

period, which includes the worst case dodge tide, have been used to determine these periods of

variance, and are represented below as percentages of times that the salinity, at 100m and 400m

from the diffuser, will exceed the regional ambient levels by 0.3, 0.6, 0.9 and 1.0 ppt (Table 10):

Table 10: Exceedance Levels at 100m and 400m for a Series of Salinity Level Increases above Ambient.

100m 400mppt above Regional

Ambient

% of Time % of Time

>0.3 37% 19%

>0.6 19% 0.5%

>0.9 1% 0

>1.0 0% 0

The 6 week period used to obtain these results can be considered representative of the exceedance

times over a complete calendar year

Spatial distribution of particular exceedance levels.

The model can also show spatial distribution of salinity levels over time, and are shown here for the

0.3, 0.6 and 0.9ppt exceedance cases:

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Figure 10: Percentage Exceedance of 0.3ppt Salinity Isopleths at the Bed Relative to Substratum Type.

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4.8.3 Far Field - Two-Dimensional

From the findings of the ADP EIS (SAW 2008) Response document, it was concluded that the

flushing and exchange of water between Gulf St Vincent and the Southern Ocean is sufficient to

ensure negligible accumulation of salt within the Gulf as a result of the ADP. The relatively small

increase in salt load from the saline concentrate discharge (compared to natural processes) and awhole of Gulf flushing rate of 3 to 4 months will allow for the sustainable operation of ADP within Gulf

St Vincent.

4.9 Outfall – Ecotoxicity

Tolerance of marine fauna to salinity variations has been assessed by ecotoxicity testing (Appendix

3). The ecotoxicity assessment was undertaken using larvae acclimatised to stable laboratory

conditions, and is therefore considered a conservative evaluation of marine biota tolerance to salinity

variations, compared to the natural environment where flora and fauna are acclimatised to seasonal

variations in temperature and salinity. In addition, a desktop review of published research has been

conducted to verify the potential ecological impact of elevated salinity. These assessments are

described below.

4.9.1 Ecotoxicity Assessment

An ecotoxicity assessment was undertaken to establish the minimum dilution rate required to avoid

adverse affects of saline concentrate and CIP chemicals on marine flora / fauna. This assessment

includes an evaluation of the potential impact of any residual chlorine in the saline discharge following

the chlorination and subsequent de-chlorination of the intake water (refer section 3.6). The calculated

safe dilution factors for the saline concentrate and the chlorinated / dechlorinated saline concentrate

indicated that the chlorination process did not significantly impact ecotoxicity of the saline

concentrate. The saline concentrate was calculated to require a dilution of 20:1 to protect 95% of

species while the chlorinated / dechlorinated saline concentrate was calculated to need a dilution of21:1 (Appendix 3).

The safe dilution factor of 20:1 equates to a salinity tolerance of 2.2ppt above ambient. This

concentration can be compared to predicted maximum salinities from the model in order to determine

the risk of harm to the environment. This is discussed further in section 4.9.3.

It should be noted that the ecotoxicity study involved exposing marine organisms to elevated salinities

for periods ranging from three to seven days, compared to predicted maximum salinity levels

averaged over 1, 6 and 24 hours

4.9.2 Ecological Assessment

The desktop review of ecological field data considers the marine habitat in the region of the outfall

diffusers, ambient salinity concentrations and the salinity tolerance of marine mammals. An extract

from WHO (2002) summarises how marine organisms acclimatise to natural variations in salinity.

Aquatic life salinity tolerance threshold

Many marine organisms are naturally adapted to changes in seawater salinity. These changes occur

seasonally and are mostly driven by the evaporation rate from the ocean surface, by rain/snow

deposition and runoff events and by surface water discharges. Typically, the range of natural salinity

fluctuation is at least ± 10% of the average annual ambient seawater salinity concentration. The “10%

increment above ambient ocean salinity” threshold is a conservative measure of aquatic life tolerance

to elevated salinity. The actual salinity tolerance of most marine organisms is usually significantlyhigher than this level.

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Salinity in excess of 10% above ambient salinity levels have been demonstrated to be a ‘crux point’ at

which development of many species starts to respond adversely. This ‘crux point’ corresponds with

the WHO (2007) prediction that most species can tolerate a 10% increase in salinity. In the case of

the Port Stanvac marine environment, with ambient salinity in the range of approx 36-38ppt during the

period 2008-2009, the WHO estimation gives a predicted upper limit tolerance of 40.6ppt, which is

significantly higher than the maximum salinity levels predicted for the ADP discharge.

4.9.2.1 Marine Habitat in the Region of the Diffuser

The benthic habitat in the region of the diffuser is characterised by a predominance of bare sand,

sparsely interspersed with red macroalgae and sea squirts (ascidians) (SARDI 2009). The biota that

are most likely to be influenced by the saline concentrate discharged into this region are the

organisms that live in the sand. These benthic infauna communities are composed of a range of

different organisms including polychaetes and crustaceans (amphipods, tanaids and isopods; Loo et

al. 2008). The infauna communities in the region of the diffuser are highly variable and are dependent

on the type of sediment in the area (coarse or fine sand). The fine sand around the diffuser area

generally supports fewer infauna animals than the coarser sand found in the deeper water (Loo et al.2008).

Figure 13: Marine Habitats Off the Coast of Port Stanvac as Identified by DEH (2008). Water quality

sampling points (A-D) and Acoustic Doppler Current Profiler (ADCP, represented as a star) locations are

included with bathymetry

4.9.2.2 Salinity Tolerance of Marine Organisms

Larvae and young individuals are particularly susceptible to elevated ambient salinity concentrations

(Einav et al., 2002). Numerous studies examining the ecotoxicological effects of increased salinity

levels upon larval development of marine organisms have concluded that there is a salinity threshold,

which when exceeded significantly influences growth and survival (Blaszkoski and Moreira, 1986;

Reynolds et al, 1976; Pillard et al, 1999).

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Certain species such as echinoderms, squid and cuttlefish are osmo-conformers that are unable to

regulate internal salinity concentrations and are therefore susceptible to changes in ambient

conditions. Sea urchins, for example, possess a permeable body wall where the gonads in the

coelomic cavity are not protected from osmotic change. As such salinity effects are likely to impact

these species more than osmo-regulating species (such as fish). Fernández-Torquemada et al.

(2005) demonstrated that echinoderms were one of the first species to disappear from a brine

discharge point when salinity was greater than 39.4 ppt. Squid (Sepioteuthis australis) and cuttlefish

(Sepia apama) eggs have also been shown to be sensitive to changes in ambient salinity

concentrations with a salinity threshold of around 44 ppt (Flinders and Adelaide University), after

which there is a significant increase in mortality.

Infauna such as polychaetes are known for the ability to adapt to environmental variation and are well

suited as indicator organisms of environmental change, as the group contains both sensitive and

tolerant species and can be utilised to show a gradient of sensitivity from pristine to heavily disturbed

areas (Del Pilar Ruso et al. 2008). Del Pilar Ruso et al. (2007) examined the spatial and temporal

effects of a brine discharge and concluded that the brine causes reduction in abundance and diversity

of infauna species (including salinity sensitive polychaetes) within the discharge zone, with theimmediate area of the diffuser characterised by a community of nematode worms where the salinity

exceeded 39ppt (background salinity in this case was usually 37.1-38.7ppt).

Other infauna species such as bivalves are better able to tolerate increases in salinity as they have

mechanisms by which to limit the saline effects. Cockles and mussels for example will stop feeding

and close their shells if conditions are unfavourable and Goolwa cockles are thought to be able to

tolerate salinities ranging from 20-45 ppt (Nell and Gibbes 1986). Tanner (in prep) showed that

juvenile metamorphosis and D-larval development of the Goolwa cockle was affected at salinities

greater than 40 ppt, with all development ceasing when salinity concentrations reached 50 ppt. Adult

ascidians (Pyura praeputialis) and brittle stars (Ophiuroidea sp.) have shown some tolerance to

increased salinity concentrations, with a salinity threshold of 44 ppt after which mortality rapidlyincreases (Beatie 2009).

There are very few studies that have examined the effects of salinity on marine plants. Most studies

have focused on species such as seagrasses as these species are considered to be more sensitive to

water quality changes. Ralph (1998); Kahn & Durako (2006) and Kerr & Strother (1985) demonstrated

that some seagrass species such as Halophila ovalis are able to tolerate elevated salinities of 25-

150% higher than background levels without significant changes to their photosynthetic response to

light. The species tended to tolerate elevated salinity concentrations better than a reduction in

ambient salinity. This has also been observed in other studies on both tropical (Lirman & Manzello

2009) and temperate (Westphalen et al. 2006) seagrass species.

A number of studies (Del Pilar Ruso, 2007,2009; Lirman & Manzello, 2009; Raventos et al. 2006;Ralph 1998; Kahn & Durako 2006) have examined the potential effects on marine species from both a

reduction and an increase in ambient salinity concentrations, due to freshwater (e.g. waste water

treatment plants and storm water) and saline concentrate discharges (desalination plants). Generally

organisms tend to be more sensitive to a reduction in salinity rather than an increase.

Work carried out for the ADP EIS (SA Water 2008) and subsequently for AA has utilised

ecotoxicology testing in order to assess the potential biological impacts that saline concentrate may

have upon marine organisms. The studies utilised where possible South Australian species and the

ADP selection of species satisfied the requirements of the ANZECC and ARMCANZ 2000 guidelines

for the assessment of toxicants in receiving waters, by having at least 5 species from four taxonomic

levels as part of the testing suite.

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4.9.3 Potential Impact of Outfall Discharge

Ecotoxicity testing has calculated a safe salinity tolerance of 2.2ppt above ambient salinity in order to

protect 95% of marine species. This tolerance was determined by assessing the observable toxicity of

the saline concentrate solution on a variety of flora and fauna species, noting that the result is likely to

be very conservative given that the tested species are acclimatised to stable laboratory conditions.

ANZECC and WHO guidelines have considered normal variations in salinity that occur naturally in

marine environment, indicating that safe salinities levels of 10% above average annual ambient to be

an appropriate guide to environmental protection. The salinity of the receiving waters in the Port

Stanvac marine environment in 2008 - 2009 averaged 36.9ppt implying a safe guideline level of

40.6ppt.

Modelling conducted for the proposed diffuser indicates a maximum salinity level for 24 hour duration

of 0.8ppt above regional ambient salinity at 100m from the diffusers. This corresponds to a “worst

case” peak salinity of 38.6ppt (2008-2009 measured ambient salinities), and would occur only during

plant production under dodge tide and no wind conditions. This information is summarised in Figure

14.

Figure 14: Comparison of Average Salinity at Port Stanvac with Predicted Salinity Levels from Mid Field

Model and Ecotoxicity Protective Salinity Concentration

The graph presented in Figure 14 illustrates the average predicted salinity per month, based on

average ambient salinity measurements for 2008/2009, and compares these with regulatory

guidelines and results from ecotoxicity testing.

Note that;

1. The

average salinities are taken from figure 10 of section 4.9.2.2

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2. The maximum predicted salinities are based on the extensive modelling discussed in

Appendix 1. These demonstrate that at 100m from the diffuser array, the maximum

predicted salinity increase averaged over 24 hours will not exceed 0.8ppt above ambient

under any of the scenarios considered.

3. The maximum predicted salinity line plotted is equal to the sum of the average measured

ambient and the predicted maximum salinity variation of 0.8ppt to illustrate the extreme

upper limit salinity levels predicted from the modelling.

4. The maximum predicted salinity of 38.6ppt remains significantly below the safe salinity

level of 40.0ppt and WHO guideline of 40.6ppt.

5. The maximum salinity line plotted is an upper limit value that could occur by a

coincidence of dodge tides, no wind driven cross currents and maximum plant

production.

5 ConclusionsThe EIS and Development Approval conditions define specific environmental and engineering

performance criteria to which AdelaideAqua D&C are required to comply. It has been demonstrated

in this report and appendices that the legal and contractual requirements for the intake and outfall

systems of the Adelaide Desalination Plant have been met.

The Intake Structure, is located within the mid benthic zone, a legal and contractual parameter, and

the grill and height arrangement minimises the risk of entrainment or entrapment of reef species,

sediment or floating debris. The seawater inflow velocity will not exceed 0.15m/s under any operating

condition. Marine biota ingress to the plant is restricted by the 75mm free spaced cupronickel grill.

Further the chemical dosing system that treats incoming seawater to remove marine microbial growth

prior to pre-treatment and the desalination process is designed as a controlled system preventing the

backflow of chemical dosing into the marine environment.

The outfall structures positioned within the prescribed envelope zone will utilise the localised

hydrodynamics assisting in midfield advection and diffusion of the diluted saline concentrate stream

without short circuiting. The physical modelling of the duckbill diffusers and the nearfield modelling of

the outfall has been discussed to demonstrate compliance with the gazetted requirement for initial

dilution. The design achieves the required initial dilution target of at least 50:1 with an equivalent 58:1

due to higher recovery rates into the local ambient water column under all current scenarios for the

full range of operating conditions and/or flows. A bypass system has been incorporated into the ADP

design as an assurance that the 58:1 criterion is met during lower plant production rates.

The outfall system design is shown to not cause environmental harm, by demonstrating that the

salinity elevations will be well within the safe dilution factors as determined by the ecotoxicity

assessments and achieve protection of species in accordance with ANZECC guidelines. Ecotoxicity

assessed the potential ecological impacts of saline concentrate discharge into Port Stanvac and

confirmed that the saline concentrate is sufficiently diluted through the outfall system. Although the

subject of further licensing approval, ecotoxicity assessments were also undertaken on CIP chemicals

to demonstrate that the discharge of neutralised CIP saline streams could

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